Interpretive Summary: Molybdenum (Mo) is an essential micronutrient for plant growth and development, and plays an important role in a variety of physiological and biochemical processes. It has been demonstrated that Mo can enhance cold resistance of winter wheat. To understand its underlying molecular mechanism, the study identified a number of proteins whose accumulation levels were differentially regulated by molybdenum treatment and/or cold treatments. Some of the proteins are involved in photosynthesis, RNA binding and protein synthesis. The research also investigated their related physiological changes in response to the treatments, and suggested that Mo might be involved in the light and dark reactions of photosynthesis and protein synthesis. The results provided an insight into molecular mechanism underlying Mo regulation at cold condition, and enable us to develop more effective strategies in application of Mo in agricultural practice to maximize winter wheat yield potential.

Technical Abstract:
Molybdenum (Mo) is an essential micronutrient for plants. To obtain a better understanding of the molecular mechanisms of cold resistance enhanced by molybdenum application in winter wheat, we applied a proteomic approach to investigate the differential expression of proteins in response to molybdenum deficiency in winter wheat leaves under low-temperature stress. Of thirteen protein spots that were identified, five spots were involved in the light reaction of photosynthesis, five were involved in the dark reaction of photosynthesis, and three were highly involved in RNA binding and protein synthesis. Before the application of cold stress, four differentially expressed proteins between the Mo deficiency (-Mo) vs. Mo application (+Mo) comparison are involved in carbon metabolism and photosynthetic electron transport. After 48 h of cold stress, nine differentially expressed proteins between the -Mo vs. +Mo comparison are involved in carbon metabolism, photosynthetic electron transport, RNA binding, and protein synthesis. Under -Mo condition, cold stress induced a more than twofold decrease in the accumulation of six differential proteins including ribulose bisphosphate carboxylase large-chain precursor, phosphoglycerate kinase, cp31BHv, chlorophyll a/b-binding protein, ribulose bisphosphate carboxylase small subunit, and ribosomal protein P1, whereas under +Mo condition cold stress only decreased the expression of RuBisCO large subunit, suggesting that Mo application might contribute to the balance or stability of these proteins especially under low-temperature stress and that Mo deficiency has greater influence on differential protein expression in winter wheat after low-temperature stress. Further investigations showed that Mo deficiency decreased the concentrations of chlorophyll a, chlorophyll b, and carotenoids; the maximum net photosynthetic rate; the apparent quantum yield; and carboxylation efficiency, even before the application of the cold stress, although the decrease rates were greater after 48 hours of cold treatment, which is consistent with changes in the expressions of differential proteins in winter wheat under low-temperature stress. These findings provide some new evidence that Mo might be involved in the light and dark reaction of photosynthesis and protein synthesis.